Wireless exploration seismic system

ABSTRACT

Systems and methods are provided for acquiring seismic data using a wireless network and a number of individual data acquisition modules that are configured to collect seismic data, and forward data to a central recording and control system. In one implementation, a number of remote modules ( 301 ) are arranged in lines. Base station modules ( 302 ) receive information from the lines and relay the information to a central control and recording system ( 303 ). Radio links operating on multiple frequencies (F 1 -F 12 ) are used by the modules ( 301 ). For improved data transfer rate, radio links from a remote module ( 301 ) leap past the nearest remote module to the next module closer to the base station.

FIELD

This invention relates to exploration seismographs, specifically toseismic survey systems where the data signals from multiple sensors aretransmitted by wireless means. The invention allows for wirelesslyreading out a seismic array, even in the case of rapidly repeatingvibrating energy source surveys, without backlogging of data or delay ofthe survey process.

BACKGROUND

Seismic surveys are often used by natural resource exploration companiesand other entities to create images of subsurface geologic structure.These images are used to determine the optimum places to drill for oiland gas and to plan and monitor enhanced resource recovery programsamong other applications. Seismic surveys may also be used in a varietyof contexts outside of oil exploration such as, for example, locatingsubterranean water and planning road construction.

A seismic survey is normally conducted by placing an array of vibrationsensors (accelerometers or velocity sensors called “geophones”) on theground, typically in a line or in a grid of rectangular or othergeometry. Vibrations are created either by explosives or a mechanicaldevice such as a vibrating energy source or a weight drop. Multipleenergy sources may be used for some surveys. The vibrations from theenergy source propagate through the earth, taking various paths,refracting and reflecting from discontinuities in the subsurface, andare detected by the array of vibration sensors. Signals from the sensorsare amplified and digitized, either by separate electronics orinternally in the case of “digital” sensors. The survey might also beperformed passively by recording natural vibrations in the earth.

The digital data from a multiplicity of sensors is eventually recordedon storage media, for example magnetic tape, or magnetic or opticaldisks, or other memory device, along with related information pertainingto the survey and the energy source. The energy source and/or the activesensors are relocated and the process continued until a multiplicity ofseismic records is obtained to comprise a seismic survey. Data from thesurvey are processed on computers to create the desired informationabout subsurface geologic structure.

In general, as more sensors are used, placed closer together, and/orcover a wider area, the quality of the resulting image will improve. Ithas become common to use thousands of sensors in a seismic surveystretching over an area measured in square kilometers. Hundreds ofkilometers of cables may be laid on the ground and used to connect thesesensors. Large numbers of workers, motor vehicles, and helicopters aretypically used to deploy and retrieve these cables. Explorationcompanies would generally prefer to conduct surveys with more sensorslocated closer together. However, additional sensors require even morecables and further raise the cost of the survey. Economic tradeoffsbetween the cost of the survey and the number of sensors generallydemand compromises in the quality of the survey.

In addition to the logistic costs, cables create reliability problems.Besides normal wear-and-tear from handling, they are often damaged byanimals, vehicles, lightning strikes, and other problems. Considerablefield time is expended troubleshooting cable problems. The extralogistics effort also adds to the environmental impact of the survey,which, among other things, adds to the cost of a survey or eliminatessurveys in some environmentally sensitive areas.

Thus, there exists a need in the art to provide improved systems andmethods for wireless seismic data acquisition. As will be appreciatedfrom the following disclosure, the systems and methods according to thepresent invention address these, and a number of other problems relatedto seismic data acquisition.

SUMMARY

The present invention provides systems and methods for acquiring seismicdata using a wireless network and a number of individual dataacquisition modules that are configured to collect seismic data andforward the data to a central recording and control system. Theinvention thus enables both a cable-less layout of the data acquisitionmodules as well as a wireless read out of the seismic data. Using acable-less layout of data acquisition modules is advantageous overconventional systems using cable communications for several reasons. Forexample, a cable-less system is not as susceptible to damage caused bywear and tear, animals, lightning strikes, etc. Additionally, acable-less system could easily be placed across rivers, highways, orother obstacles, whereas it is difficult to implement a seismic surveysystem that uses cables in these areas. Moreover, cable based seismicsurveys require a relatively large number of vehicles and manpower totransport and lay cables spanning several square kilometers.

The ability to capture the data wirelessly is potentially advantageousas well. For instance, when a single cable is damaged, all data fromremote data acquisition modules located on the distant end of thedamaged cable may be lost. This type of problem is not present insystems where the seismic data is transmitted wirelessly. In particular,rerouting the data is much more feasible using a wireless network, whichpotentially provides for a more reliable system.

Certain proposed cable-less and/or wireless seismic acquisition systemshave required manual read outs or have otherwise involved a read outprocedure that resulted in delaying the seismic survey process. It hasbeen recognized that it is important to provide for capture of data froma wireless array in a manner that avoids backlogging of data or delayingthe survey process. That is, the system can operate much moreefficiently and inexpensively if the data capture can be accomplishedwithout delaying the survey process (e.g., without delaying subsequentseismic events). Conventionally, the survey process involves placing anarray of vibration sensors (accelerometers or velocity sensors calledgeophones) on the ground, typically covering several square kilometers.Then a vibration/seismic event may be propagated through the earth anddetected by these sensors. Signals from the sensors are captured andanalyzed by a processing unit. Most commonly, seismic events are createdby one of two methods. First, explosives may be used to generatevibrations in the earth. Alternatively, a vibrating energy sourcevehicle may be used. A vibrating energy source vehicle is a vehicledesigned for creating vibrations in the ground. Typically, a vibratingenergy source vehicle will create a vibration in one location for ashort period of time (e.g., fifteen or twenty seconds). Then, thevehicle may move to another location nearby and immediately begingenerating another vibration. There may only be a few seconds betweeneach vibration event. This process may continue for several hours untilthe desired amount of seismic data is acquired. The survey process isvery expensive in terms of the required amount of equipment andmanpower, so any delays in the measurement process are extremely costly.Thus, it will be appreciated that the seismic data is preferably eitherstored locally for the entire survey, or otherwise transferred, forexample, to a central storage system, at a rate sufficient toaccommodate the operation of the vibration source without causing adelay.

In addition to the items noted above, there are a number of attributesthat have been recognized as being useful to provide a commerciallydesirable wireless seismic survey system. These attributes include thefollowing:

1. The system cost should be approximate to or less than that of a wiredsystem.

2. The system should perform in uneven terrain and around or overobstacles, across an area measured in square kilometers.

3. The system should be usable worldwide without complex radio licensingissues.

4. Power consumption should be low enough that handling and replacingbatteries does not create undue logistic problems.

5. Seismic data should be made available for inspection in nearreal-time to ensure quality and avoid the need to repeat some or all ofthe seismic data acquisition.

6. The system should be capable of scaling up to thousands of sensors.

7. The system should meet the technical performance specifications ofcontemporary wired systems.

Various aspects of the present invention involve a wireless transferprotocol to enable the capture of seismic data from a seismic arraywithout delaying the seismic survey. In this regard, it will be notedthat the volume of data generated by an array of vibration sensors maybe significant. For instance, if each vibration sensor acquires 500samples per second with a resolution of 24 bits per sample, the samplesize for each sensor is 12,000 bits per second. For a 20 secondvibration (i.e. seismic event) the resulting sample size is 240K bitsper sensor. It is not uncommon for a plurality of sensors to be alignedinto lines or strings that contain a hundred or more sensors. Further,multiple lines or strings may be disposed in parallel to define an arrayof sensors that cover a desired geographic area. For a seismic surveythat utilizes 1000 sensors, 240,000,000 bits of data may be generatedfor each seismic event. Accordingly, the wireless transfer of all thedata from the sensors to a central recording system(s) at a ratesufficient to keep up with the seismic events can be problematic due tolimited bandwidth. In one implementation of the present invention,individual data acquisition modules transmit seismic data to aneighboring or near neighboring module, which, in turn, relays thereceived seismic data, together with its own data, on to a furthermodule. This process of data forwarding continues until the data reacheseither a line tap or a central recording and control system. Thisarrangement is desirable for several reasons. First, since the dataacquisition modules are only transmitting data to nearby modules, ratherthan directly to a central location, relatively low power transmissionscan be utilized. The savings in power allows the modules to operatelonger without battery replacement, and/or to operate using batterieswith a smaller capacity. Additionally, low power transmissions reach asmaller area, which allows fewer channels to be utilized (or availablechannels to accommodate a larger number of acquisition modules) becausethey can be reused in different areas of the array without interference.Additionally, the use of lower power signals may enhance module locationinformation using signal strength based techniques. It will beappreciated, however, that it is problematic to reconcile the desire forsuch serial data transfer with the desired read out rates as describedabove. These potentially conflicting objectives are addressed by theinvention as set forth herein.

In accordance with one aspect of the present invention, a seismic arrayis provided that can wirelessly read out an array using serial datatransfer at a rate sufficient to avoid delaying operation of a vibratingenergy source. As noted above, a vibrating energy source typicallyvibrates for a few seconds to define a seismic event, then moves toanther location and immediately starts vibrating again. This cycle maybe repeated in only a matter of seconds, e.g., 20-30 seconds. It isdesirable to read out the resulting seismic data to a base station orthe like in serial fashion such that each module needs only tocommunicate with a neighboring or near neighboring module, and lowtransmission powers can be used. However, serial data transfer generallyinvolves increasing data transfer rate requirements, as a function ofthe length of the serial data transfer path, for a given overall arrayread out time.

The present aspect of the invention provides a method and apparatus(“utility”) that involves providing an array for obtaining seismic datacorresponding to operation of a repeating vibrating energy source. Aread out mechanism is provided in connection with the array that definesat least one serial data transfer path for reading out the seismic data.The read out mechanism is operated to read out the array at a ratesufficient to avoid delaying operation of the vibrating energy source.For example, the read out mechanism may be operative to read out aserial data transfer path involving multiple modules (e.g., more thanabout 10 modules) in no more than about 20 seconds.

In accordance with another aspect of the present invention, more thanone seismic data acquisition module in a given serial data transfer pathcan transmit data simultaneously. As noted above, serial data transferpaths are desirable but can result in increased data transfer raterequirements. In order to address this potential issue, more than onemodule in a serial data transfer path can transmit at a time, forexample, by employing an appropriate multiplexing mechanism to avoidinterference. Thus, a utility in accordance with the present aspect ofthe invention involves: providing an array including at least one serialdata transfer path, where data is serially transferred between multiplemodules in route to a base station or other collection point; andoperating the array such that at least two of the multiple modules onthe serial data transfer path transmit concurrently. In this manner,higher duty cycles can be achieved for individual transmitters,resulting in enhanced read out efficiency.

In accordance with yet another aspect of the present invention,different modules on a given serial data transmission pathway of aseismic array use different transmission frequencies. Again, serial datatransmission pathways are desirable but can raise certain issuesrelating to array read out rates. These issues can be addressed by usingmultiple frequencies in a single serial data transfer path so as to, forexample, allow for frequency division multiplexing. A correspondingutility in accordance with the present aspect of the invention involves:providing an array including at least one serial data transfer path,having multiple modules; and operating the array such that a firstmodule on the serial data transfer path transmits at a first frequencyand a second module on the serial data transfer paths transmits at asecond frequency different than the first frequency. For example,different frequencies can be assigned to all modules within receivingrange of one another that transmit concurrently.

In accordance with another aspect of the present invention, multiplemultiplexing mechanisms are implemented in connection with a serial datatransfer path of a seismic array. For example, each multiplexingmechanism may allow for coordinated operation of the transmitters of theserial data transfer path to enable improved read out rates withoutundue interference. In one implementation, both time divisionmultiplexing and frequency division multiplexing are used in connectionwith a serial data transfer path. For example, the time divisionmultiplexing may be implemented such that only one-half (or one-third,one-fourth, etc.) of the transmitters in the serial data transfer pathare transmitting in any defined time interval. Those transmitters thattransmit at the same time (or at least those transmitting at the sametime and within receiving range of a receiver in the pathway) can beassigned different frequency channels and/or can utilize anothermultiplexing mechanism such as code division multiplexing. Wheremultiple serial pathways are present in the array, such multiplexing canalso be implemented so as to avoid interpathway interference.

In order to facilitate the capture of seismic data from an array ofseismic data acquisition modules while avoiding delays in the seismicsurvey process, it may be desirable to provide synchronized transmissionof seismic data from a number of acquisition modules that utilize acommon wireless serial data transmission path for reporting seismicdata. That is, along a serial data transmission path defined by a numberof acquisition modules, a first subset of the acquisition modules may beoperative to simultaneously transmit seismic data to a second subset ofthe acquisition modules. Such an arrangement may allow for simultaneoustransfer of seismic data from a number of upstream acquisition modulesto a number of downstream acquisition modules that are located nearer toa data collection point (e.g., line tap or base station). For instance,every other acquisition module in a serial data transfer path may beoperative to transmit seismic data to an adjacent downstream acquisitionmodule during a first time interval. Likewise, when the downstreamacquisition modules receive data from an adjacent upstream module, thedownstream modules may transmit the received data and/or additionalseismic data further downstream during a second interval. Accordingly,by repeating the process multiple sets of seismic data may besimultaneously transferred step-by-step from a plurality of acquisitionmodules to one or more base stations and/or a central recording andcontrol system.

In order to effect such simultaneous transfer of seismic data from aplurality of acquisition modules, one aspect of the present inventionprovides a utility for transmitting seismic data. The utility involvesdisposing multiple seismic data acquisition modules in an array whereeach acquisition module is operative to wirelessly communicate with atleast one other acquisition module in the array. Accordingly, suchcommunication between the acquisition modules allows for defining a datatransmission path through the array. A base station is provided that isoperative to receive seismic data from at least one acquisition modulein the array. In this regard, the base station is in wirelesscommunication with the data transmission path. In order to transmitseismic data from the plurality of acquisition modules, the utilityfurther involves first transmitting first seismic data from at least afirst module of a first subset of the acquisition modules to at least afirst module of a second subset of the acquisition modules during afirst transmission period. After the first transmission period, thefirst seismic data may be transmitted from the first module of thesecond subset of acquisition modules to a second module of the firstsubset of acquisition modules during a second transmission period. Inthis regard, the first set of seismic data may be relayed by the datatransmission path towards the base station.

In order to transmit the data towards the base station, during each ofthe transmitting steps, individual acquisition modules may transmitseismic data to another seismic data acquisition module that is locatednearer to the base station. In this regard, the data may be relayed fromremotely located acquisition modules to acquisition modules that arelocated nearer to the base station. Further, one or more acquisitionmodules located within the transmission range of the base station maytransmit the seismic data to the base station.

In addition to re-transmitting the first seismic data received from thefirst module of the first subset, the first module of the second subsetmay be operative to append additional seismic data (i.e., generated bythe first module of the second subset) to the second module of the firstsubset. In this regard, during each transmitting step, additional datamay be appended to the seismic data received from a remotely locateddata acquisition module. Accordingly, the first and second transmittingsteps between the first and second subsets of acquisition modules may berepeated for additional modules of each subset until all seismic datafrom the plurality of acquisition modules is received by the basestation.

In any arrangement, each seismic data acquisition module is operative togenerate seismic data in response to a seismic event. In the case of avibrating energy source, the event may last several seconds (e.g., 20seconds). Accordingly, it may be desirable to begin data transmissionprior to the end of the seismic event. That is, initiating datatransmission before the seismic event ends may significantly reduce thetime required to complete the transmission of the entire data setcollected for the seismic event. Such transmission may be completedsubstantially in real-time or prior to the initiation of a secondseismic event. In order to effect such transmission during the seismicevent, each acquisition module may be operative to packetize seismicdata as it is generated. Resulting packets (e.g., of a predetermineddata size or temporal period) may include information identifying theacquisition module that generated the data as well as the acquisitiontime for the packet. The packet may then be relayed to the base station(e.g., via one ore more relays), to a central control and storage systemor another location where the packets may be stored and/or reassembled.That is, multiple packets from individual seismic acquisition modulesfor a single seismic event may be reassembled into a single data file ata location removed from the acquisition modules.

In one implementation, in order to facilitate the simultaneous transferfrom the first subset of acquisition modules to the second subset ofacquisition modules, each of the plurality of seismic data acquisitionmodules is assigned a transmission frequency for use in transmitting theseismic data. Further, due to the potentially large number ofacquisition modules forming a single serial data transmission path, itmay be desirable and/or necessary to assign first and second seismicdata acquisition modules within a serial transmission path a commontransmission frequency. That is, due to limited available transmissionfrequencies, it may be useful to reuse one or more frequencies. Thetransmission power and/or physical spacing of the modules may beselected so as to prevent interference between modules having a commontransmission frequency. Moreover, when a common frequency is reused in asingle serial data transmission path for a common transmission period,it may be desirable that the modules utilizing the common frequency areseparated by a distance that is greater than the transmission range ofthe modules. It will be appreciated that modules utilizing a commontransmission frequency may further be arranged such that they transmitseismic data during temporally distinct transmission periods or so thatthey utilize a further multiplexing mechanism, such as code divisionmultiplexing, to reduce or avoid interference. The spacing and/ortransmission power of the acquisition modules may also depend ontransmission frequencies in one or more adjacent transmission pathsutilized to transmit seismic data from additional arrays.

According to another aspect of the invention, a utility is provided forenhancing a data transfer rate between a plurality of seismic dataacquisition modules defining an array and a base station that isoperative to gather seismic data from the array by coordinating theoperation of multiple modules that communicate directly with the basestation. The utility involves disposing a plurality of seismic dataacquisition modules in a physical path e.g., a line of modules. In thisregard, each seismic data acquisition module in the physical path isoperative to wirelessly communicate with at least one other seismic dataacquisition module in the path such that the data is seriallytransferred from remote modules to modules located nearer to the basestation. First and second serial data transfer paths are defined throughthe physical path. These first and second (or additional) data transferpaths may be formed by alternate or other pattern of acquisition modulesalong the length of the physical path. Accordingly, the first and seconddata transfer paths are each operative to relay data for the modulesthat form each path, and the base station is preferably operative toalternately receive transmission of seismic data from the first andsecond transmission paths. In this regard, the base station may beoperative to substantially continually receive transmissions of seismicdata from the first and second transmission paths. For example, the basestation may be operative to alternately receive transmissions from thefirst and second paths so that the base station receiver has asubstantially 100% duty cycle.

According to another aspect of the invention, a utility is provided forrelaying seismic data through a series of acquisition modules where agiven module uses different frequencies for receiving and transmittingdata. The utility utilizes a plurality of seismic data acquisitionmodules that are disposed in a series and are operative to wirelesslycommunicate with at least one upstream acquisition module and at leastone downstream acquisition module for the purposes of relaying seismicdata therebetween. In this regard, the seismic data acquisition modulesare typically operative to receive upstream seismic data from at leastone upstream seismic data acquisition module and transmit the upstreamseismic data to a downstream seismic data acquisition module. Further,to effect transmission of multiple sets of upstream data to multiplesets of downstream acquisition modules, it may be useful to assigndifferent transmission and receiving frequencies to each of the dataacquisition modules. Typically, this will require that any individualdata acquisition module be operative to receive upstream data on a firsttransmission frequency and provide the upstream data, as well as anydata generated by the receiving acquisition module, to a downstreamacquisition module on a second transmission frequency.

Accordingly, each individual acquisition module may be tuned to areceiving frequency associated with an upstream acquisition module andtuned to a transmitting frequency that corresponds to receivingfrequency of a downstream acquisition module. A single antenna ormultiple antennae may be used in this regard. The acquisition module maybe operative to receive transmissions from an immediately adjacentupstream acquisition module and provide data to an immediately adjacentdownstream acquisition module. In another arrangement, the acquisitionmodule may be operative to receive transmissions from a non-adjacentupstream acquisition module and transmit to a non-adjacent downstreamacquisition module. In this regard, receptions and transmissions mayskip adjacent acquisition modules such that first and second serial datatransmission paths are interleaved within a physical path of seismicacquisition modules.

In accordance with another aspect of the invention, at least some of themodules are configured to be self-locating. In order for the datacaptured by the sensors to be processed, the geographic location of eachsensor must be determined. Rather than manually measuring the locationof thousands of sensors as has been previously done, the presentinvention may use various methods to determine the location of at leastsome of the modules automatically. For example, in one embodiment, eachmodule may include a Global Positioning System (GPS) receiver. Themodules may use the receiver to self-locate, and further may wirelesslytransfer the location data to a central recording system.

In another embodiment, only some or none of the modules or base stationsmay be equipped with GPS receivers. The system may advantageously use RFtechnology to determine the location of at least some of the modules.For example, a module or base station may propagate a signal from itstransmitter to several other remote modules. The other modules or basestation(s) may individually record the time that the signal was receivedfrom the first module or base station and/or the strength of the signal.Using the time the signal was received at each remote module, thedirection from which the signal was received, the signal strength orother parameters, the location of the module may be determined. Thus, ifthe location of one or more modules or base stations is known, thelocation of the remote module propagating the signal can be determined.It will be appreciated that this aspect is not limited to using oneparticular RF based method to determine the location of a remote module.A person skilled in the art will recognize that there are a number ofmethods that utilize RF technology that may be employed as will bediscussed in more detail below. Moreover the location of the module maybe determined based on signals received at the module from other modulesor base stations, or the location of the module may be determined basedon signals transmitted from the module to other modules or base stations(e.g., the technology may be module-based or external).

In yet another embodiment, RF methods of location may be used incombination with GPS methods. For example, a fraction of the modulesand/or base station may include GPS receivers. Since GPS methods give anaccurate location, these modules or base stations may be used asreference locations. Then, the reference locations may be used tocalculate the actual location of other modules that are not equippedwith GPS receivers using the relative location calculated using RF basedmethods. For example, only the base stations (or a subset thereof) mayinclude GPS receivers. In another example, all modules may include GPSreceivers. Then, both RF based location methods and GPS methods may beused in tandem to ensure an accurate location measurement.

An advantageous feature of the present invention is the capability torecord the location of the remote modules at a central recording andprocessing system in near real-time. That is, it is not necessary totravel to each module to extract the location data. Instead, the remotemodules, or other location platforms, may be configured to wirelesslytransmit the location data back to a central control and recordingsystem. The location data may be transferred across the same networkused to transfer the seismic data, or a separate network may beutilized. Moreover, different frequencies, powers, or other signalparameters may be used for the location signals (in relation to theseismic data transfer signals). It will be appreciated that the locationof the modules need not be resolved prior to the initiation of seismicdata acquisition. Rather, the location can be resolved contemporaneouslywith or subsequent to seismic data acquisition.

In accordance with a still further aspect of the present invention,module self-locating technologies may be employed that take advantage ofthe wireless seismic array context to determine location. As notedabove, it has been recognized that it is important to provide for theautomatic determination of location of the remote data acquisitionmodules, for example, using RF location techniques, embedded GPS, acombination of the two, or other suitable methods. Generally,determining the precise location of potentially thousands of dataacquisition modules is a costly and time-consuming task. First, workersgenerally travel to each data acquisition module and determine thelocation using a GPS receiver or a similar device. This requires firstthat workers know the general location of each module so that it can befound. Once the module is found, it often takes a considerable amount oftime for the GPS receiver to provide an accurate location measurement.The location of each device must be entered into a computer system whereit will be used when the data is processed. The time spent locating thedevice, waiting for GPS data, and storing the location data can besubstantial. Furthermore, this process may be repeated for thousands ofsensors. Therefore, a system that provides for the automated location ofthe data acquisition modules substantially without contemporaneous humaninteraction is advantageous. The present invention provides for theautomatic locating of at least some of the modules, thus reducing set-upcosts. Any suitable self-locating technology can be used in this regard,including GPS location systems built into the modules and capable ofwirelessly reporting location.

However, it has been recognized that the wireless nature of theacquisition modules provides additional self-location possibilities. Inparticular, a number of RF-based location technologies have beendeveloped in connection with wireless telephony and mesh networks.Generally, these technologies involve multilateration (such astriangulation) algorithms using ranging and/or directionalityinformation derived from multiple signals, such as time difference ofarrival (TDOA), angle of arrival (AOA), signal strength, etc.

In particular, it has been recognized that these technologies can beadapted to the present wireless data acquisition context. The existingtechnologies are based on a paradigm involving many mobile handsets anda smaller number of fixed network structures such as wireless networkbase stations. The goal of these systems is generally to locate themobile handsets and the locations of the fixed network structures areknown. Oftentimes, however, the handsets have limited contact with thefixed structures due to distance, buildings or other obstructions andlocal topology, resulting in the inability to accurately and timelylocate the handsets. Additionally, as the handsets are mobile, thelocation signals must generally be obtained substantiallysimultaneously. As a result, in many cases, handsets cannot be locatedusing such technologies or the location is subject to largeuncertainties.

This would seem to make such technologies unattractive for locatingacquisition modules in the present context, particularly given theaccuracy required. However, a number of factors render thesetechnologies viable in this context if properly adapted. First, many RFtransmitters can be made available in a close proximity to anacquisition module to be located, thereby allowing for high spatialresolution multilateration algorithms. In addition, if desired, a numberof these RF transmitters can be accurately located using GPS or othertechnologies and can thereby serve as fiducial references to anchor themultilateration calculations. Moreover, the acquisition modules arestationary, allowing for execution of statistical processing over timeto reduce uncertainties in the multilateration techniques. The fiducialreferences can also be located to ensure uninterrupted communication ofthe RF location signals. It will be appreciated that the locationcalculations can be performed at the acquisition modules (e.g., based ondedicated location signals or other signals received form multipletransmitters) or at another location (e.g., based on dedicated locationsignals or other signals transmitted from a module and received atmultiple receivers).

Another aspect of the present invention involves a utility for designinga wireless seismic survey using parameters that are unique to wirelessseismic survey systems. For example, the layout of the remote dataacquisition modules is not constrained by a physical connection betweeneach module, as is the case in a conventional cable-based system. Thismay enable the system designer to have more freedom when choosing thelayout of the modules. For instance, there may be a need to place themodules in a configuration so as to avoid an obstruction. Additionally,parameters relating to the characteristics of wireless transfer may beused to design the wireless seismic survey (e.g., transmit power, numberof channels, bandwidth, etc.). As an example, the transmit power and/orthe distance between the modules may be increased or decreased to meetthe particular survey's objectives. Furthermore, the number of wirelesschannels required to transfer the seismic data may depend on the spacingof the remote data acquisition modules. Moreover, the number and spacing(density) of acquisition modules may differ, in relation to conventionalwired arrays, due to economies associated with the wirelessimplementation that affect the economic tradeoffs between the cost ofthe survey and number of sensors. Accordingly, the utility according tothe present aspect of the invention involves: obtaining parameterinformation regarding potential array configurations, wherein the arrayconfigurations are a function of the characteristics of wireless datatransfer systems; obtaining survey objective information regarding aseismic survey under consideration; and determining an arrayconfiguration based on the parameter information and survey objectiveinformation.

Yet another aspect of the present invention involves receiving seismicdata from a rapid read out (e.g., read out between seismic events)wireless seismic survey system and processing the data into a form thatis useful for analyzing the characteristics of one or more subsurfacegeologic structures. The receiving step may include, for example,transferring the seismic data to a computing system that is capable ofprocessing the data. The processing step may include a number of methodsfor manipulating the seismic data (e.g., filtering, summing,synchronizing, displaying, normal move out, executing a common mid-pointor other gather etc.). It will be appreciated that this may furtherinvolve particular processing unique to the wireless context such asdeinterleaving of data from the different modules and accounting forunique wireless array geometry. Additionally or alternatively, theprocessing step may include interpreting the seismic data to identifythe characteristics of one or more subsurface geologic structures.

DRAWINGS

For a more complete understanding of the present invention and furtheradvantages thereof, reference is now made to the following detaileddescription taken in conjunction with the drawings, which are brieflydescribed below.

FIG. 1 shows a typical layout of sensors and cables in a wired seismicsystem.

FIG. 2 is a block diagram of the remote data acquisition and relaymodule in accordance with an embodiment of the present invention.

FIG. 3 is a typical layout of modules and sensors in the wireless systemin accordance with an embodiment of the present invention.

FIG. 4 is a detailed drawing of a portion of the wireless system use todiscuss frequency allocation and operation in accordance with anembodiment of the present invention.

FIG. 5 illustrates a system for automatically determining the locationof data acquisition modules.

FIGS. 6A-6C illustrate the operation of various technologies that can beused to automatically locate the data acquisition modules.

FIG. 7 illustrates a layout of modules in the wireless seismic surveysystem in accordance with an embodiment of the present invention.

FIG. 8 illustrates an alternative layout of the seismic array and anassociated read out protocol in accordance with the present invention.

FIGS. 9A-9C illustrate certain self-locating structure and functionalityin accordance with the present invention.

FIG. 10 is a flowchart illustrating a process for designing a wirelessseismic array in accordance with the present invention.

FIG. 11 is a flowchart illustrating a process for processing data from awireless seismic in accordance with the present invention.

FIGS. 12A-C illustrate a process for transferring data along a serialdata transfer path of a wireless seismic array in accordance with thepresent invention.

DETAILED DESCRIPTION

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that it is not intended to limit the inventionto the particular form disclosed, but rather, the invention is to coverall modifications, equivalents, and alternatives falling within thescope of the invention as defined by the claims.

In certain implementations as described below, the present inventioncombines the data acquisition function and radio relay function into asingle module, thus solving a number of problems. Each module typicallyrelays the data to another module en route to the central control andrecording system. Some of the advantages of one embodiment of thepresent invention include:

(a) Because the space between modules is small, typically no more thanabout 50 meters, relatively low power radios can be used to relay theinformation to the next module. The savings in power allows the modulesto operate for several days on flashlight batteries or even longer onsolar cells. Additionally, batteries could be replaced or rechargedduring scheduled relocation of the modules.

(b) Low-cost, integrated-circuit radio chips are available allowing adesign that costs less to manufacture than systems with cables runningbetween modules in a wired system.

(c) Because the array of acquisition modules is laid on the terrain as amesh, it automatically adapts to uneven terrain. If an obstructionexists, a spare module can be used to pass the signal over or around theobstruction.

(d) If the 2.4 GHz frequency band is chosen, it will be legal in mostareas of the world to operate at these low power levels. Because seismicsurveys are normally conducted in remote areas, interference fromexternal sources should not be a problem.

(e) By operating the modules on different frequencies within this band,the modules may continuously pass data down a seismic array like a“bucket brigade,” providing real time data acquisition and relay to thecentral control and recording system.

(f) The network may be expanded in scale by adding modules and extendingthe array to accommodate thousands of modules.

FIG. 1 depicts a common physical layout of a conventional seismicsurvey. A number of remote data acquisition modules 101 are connected bycables in a line and arrayed on the ground. Connected to each of themodules is one or more sensors configured as individual sensors,multi-component sensors, or strings of sensors wired into groups. Eachof the modules may contain electronics to amplify, digitize, and storethe signals from the sensors, or in the case of digital sensors, collectand store the data. The remote data acquisition modules may containadditional circuitry to test the sensors and/or the acquisitioncircuitry to ensure proper function and performance.

The remote modules are connected together in a line by electrical orfiber optic cables, and the line is connected to a second device calleda “line tap” or “crossline unit” 102. The line taps are then connectedtogether in a string, and eventually to a central control and recordingsystem 103.

Seismic data is generally acquired and passed down the cables from theremote data acquisition modules to the line taps, and thence to thecentral control and recording system. Instructions and timing signalsare passed up the cables from the central control and recording systemto the line taps and thence to the remote data acquisition modules.Other geometries may be used, including just a linear array. Redundantlines or a ring topology may be used to provide alternate data andcontrol paths in the event of failures or obstructions. The number ofsensors deployed may vary considerably depending on the requirements ofthe survey. If one of the lines must be discontinuous because of someobstruction, such as a river, a radio frequency communication system maybe inserted to carry the data and instructions across the gap.

The central control and recording system usually consists of a computerwith a display, keyboard, interface to the line tap string, and digitalstorage system. In one implementation, the central control and recordingsystem might consist of a standard notebook computer with an Ethernet,USB, or wireless interface to connect to a line tap string or to aninterface device that connects to the line tap string. Data may bestored on the computer's internal hard disk. For larger systems, thecentral control and recording system might consist of a larger computerwith separate display and keyboard and separate storage device such as atape drive, one or more hard disks, or some other storage deviceconsistent with storing relatively large amounts of data.

In the present invention, wireless data acquisition and relay modulesreplace the conventional wired units. The positions of the remotemodules might be the same as in a wired system, or the array might beadapted to exploit the flexibility of a wireless system. In thefollowing discussion, a generalized example is first provided toillustrate the flexibility of the present system. That is, theacquisition modules can be arranged in substantially any pattern andserial communications of seismic data can occur along substantially anyroute in order to report information to a central control and recordingsystem. Thereafter, specific examples are provided that illustrateadvantageous array configurations and read out protocols.

FIG. 7 shows a layout of a wireless seismic survey system 700 inaccordance with one embodiment of the present invention. The system 700includes data acquisition modules 701 which are distributed throughout aseismic survey site. The data acquisition modules 701 are configured tocommunicate with surrounding modules through wireless links 707.Generally, seismic data is wirelessly forwarded from data acquisitionmodules 701 that are more remotely located to a central control andrecording system 703 to those that are less remote until the datareaches the central control and recording system 703. As shown, the datamay be forwarded by the data acquisition modules 701 until it reaches abase station 705. This base station may be capable of transferring andreceiving data between the central control and recording system 703 byany suitable method (e.g., Ethernet, USB, fiber-optic link, somecomputer compatible wireless interface such as IEEE 802.11, etc.).Additionally the base stations 705 may simply be data acquisitionmodules that are configured to communicate directly with the centralcontrol and recording system 703.

FIG. 7 illustrates that the layout of the data acquisition modules neednot be a linear array, or any regular geometric configuration. This isadvantageous because it allows the survey system to operate aroundobstructions, and allows freedom for survey designers to choose a layoutthat will optimize the performance of the system.

It will be appreciated that the data path of the seismic data betweenthe data acquisition modules may be manually or automaticallyconfigured. In the former case, each module may be programmed, forexample, to communicate with predetermined modules that will be placedimmediately or closely adjacent to each other. Alternatively, themodules may be configured to automatically detect and select an optimalpath for the seismic data to be transferred. In this latter case, themodules may be positioned without needing to place particular modules inparticular locations. Then, the modules may select an optimal data pathbased on various factors such as obstructions, signal strength, transferrates, etc.

An important aspect of the present invention is the capability toprovide for rapid capture of data from a wireless array. That is, thesystem can operate more efficiently and inexpensively if the datacapture can be accomplished without delaying the survey process, asdescribed hereinabove. In order to achieve this goal, it will beappreciated that the seismic data needs to either be stored locally(e.g., at a module base station or other collection station), in wholeor in part, for the entire survey, or otherwise transferred to a centralcontrol and recording system in a manner which does not interfere withor delay the operation of the vibration source device. The presentinvention provides a system for wireless transfer of seismic data whichachieves this goal. In one embodiment of the present invention, all ofthe seismic data for a seismic event is transferred from the dataacquisition modules to the central control and recording system, orother storage system, in no more than about 20 seconds, from the end ofthe vibration event. This is achieved by selecting data transfer rates,the number of data acquisition modules in the array and in each serialdata transfer line, and other factors. An example of a preferredembodiment is described in detail below.

FIG. 2 shows a block diagram of a wireless remote acquisition and relaymodule 200 in accordance with an embodiment of the present invention. Avibration sensor 201 converts vibrations into electrical signals whichare fed through switch 210 to preamplifier 202 and thence to the analogto digital (A/D) converter 203. The digital data from the A/D converter203 is fed into the Central Processor 204 or directly into a digitalmemory 205. Alternately, in the case of a sensor 201 with direct digitaloutput, the signals may flow directly to the processor 204 or memory205.

In addition to controlling the system and storing the data in thememory, the processor 204 may perform some calculations on the dataincluding decimation, filtering, stacking repetitive records,correlation, timing, etc. The remote module 200 may also receiveinformation through the transceiver 206, for example: timinginformation, cross-correlation reference signals, acquisitionparameters, test and programming instructions, location information,seismic data from upstream modules and updates to the software amongother commands. The transmit and receive signals couple through antenna207.

The processor 204 can control the transceiver 206, includingtransmit/receive status, frequencies, power output, and data flow aswell as other functions required for operation. The remote module 200can also receive data and commands from another remote module or basestation, store them in the memory, and then transmit them again forreception by another remote module up or down the line.

A digital-to-analog (D/A) converter 208 may be included in the systemwhich can accept digital data from the processor 204 to apply signalsthrough a switch 210 to the input circuitry. These signals, which mayfor example consist of DC voltages, currents, or sine waves, can bedigitized and analyzed to determine if the system is functioningproperly and meeting its performance specifications. Typical analysismight include input noise, harmonic distortion, dynamic range, DCoffset, and other tests or measurements. Signals may also be fed to thesensor 201 to determine such parameters as resistance, leakage,sensitivity, damping and natural frequency. The power supply voltage mayalso be connected through the switch 210 to the A/D converter 203 tomonitor battery charge and/or system power. The preamplifier 202 mayhave adjustable gain set by the processor 204 or other means to adjustfor input signal levels. The vibration sensor 201 may be a separategeneric unit external to the remote module 200 and connected by cables,or the sensor 201 might be integral to the remote module package.

If the remote module 200 is to be used as a base station, equivalent toa “line-tap” or interface to the central recording system, it will alsohave a digital input/output function 211 which may be, for example, anEthernet, USB, fiber-optic link, or some computer compatible wirelessinterface (e.g., one of the IEEE 802.11 standards) or another means ofcommunication through a wired or radio link. It may be acceptable to uselarger battery packs for the line tap wireless data acquisition andrelay modules because they will normally be relatively few in number andmay communicate over greater distances using a high speed datacommunication protocol.

The remote module 200 is constructed of common integrated circuitsavailable from a number of vendors. The Transmit/Receive integratedcircuit 206 could be a digital data transceiver with programmablefunctions including power output, timing, frequency of operation,bandwidth, and other necessary functions. The operating frequency bandmay preferably be a frequency range which allows for unlicensedoperation worldwide, for example, the 2.4 GHz range. The CentralProcessor 204, Memory 205, and switch 210 can include any of a number ofgeneric parts widely available. The A/D converter 203 could preferablybe a 24-bit sigma delta converter such as those available from a numberof vendors. The preamplifier 202 should preferably be a low-noise,differential input amplifier available from a number of sources, oralternatively integrated with the A/D converter 203. The D/A converter208 should preferably be a very low distortion unit which is capable ofproducing low-distortion sine waves which can be used by the system toconduct harmonic distortion tests. The module 200 may include a numberof other components not shown in FIG. 2, such as a directional antennaefor AOA signal measurements, separate transmit and receive antennae,separate antennae for location signals and seismic data transfersignals, GPS receivers, batteries, etc.

The following example depicts how the system can acquire seismic datacontinuously. Assume that every module is sampling the vibration signalsat 500 samples per second with a resolution of 24 bits per sample. Theseismic data from the vibration sensor is digitized and stored inmemory. While this is taking place, the transceiver 206 is receivingdata from the next module more remotely located to the central recordingsystem. After some amount of data is collected from the sensor 201 andthe other modules, the module switches to transmit mode and sends somepackets of data collected from the sensor 201 and the other modules ontowards a module closer to the central recording system. Each packet ofdata is also annotated with some identification as to the originalsource sensor and the time acquired. The module continues to acquire andstore data during the transmit phase so there are no gaps in the record.

The time stamp annotation may come from a clock in the microprocessor orthe radio. The clocks in all the modules may be periodically adjustedand synchronized with a signal from the central recording system orother source.

FIG. 3 shows one possible configuration of a wireless seismic system inaccordance with an embodiment of the present invention. A number ofremote modules 301 may be arranged in lines as is done with a wiredsystem as shown in FIG. 1, except that there is no physical connectionbetween the remote modules. Replacing the line-tap modules are basestation modules 302 which may be connected to a central control andrecording system 303 by Ethernet, fiber optic, or other digital datalink or a wireless substitute. Example radio links operating onfrequencies F1 to F12 are indicated by arrows. Note that for improveddata rate, each radio link in the illustrated embodiment leaps past thenearest remote module to the next module closer to the base station.Other radio transmission paths are possible, including direct to thenearest remote module, leaping multiple modules, or in the case of anobstruction or equipment fault, past a defective remote module or evenacross to another line or any other logical path that establishes acommunication flow. The central control and recording system may be anotebook computer or larger equivalent system.

FIG. 4 is an exploded view of a portion of the line representative of anarray of wireless remote modules Rn and base stations BSn connectedtogether by an Ethernet or Fiber Optic or radio frequency wireless orother link in accordance with an embodiment of the present invention.During the data acquisition phase, signals from the sensors will bedigitized and stored in memory. Some of the remote modules will thentransmit digital data from the memory through the RF link. Others willbe receiving digital data from nearby modules, temporarily storing datain memory. At maximum data transmission rate, half the remote modulesmay be transmitting and half would be receiving at any time. So that themodules don't interfere with one another, different frequencies may beassigned to each remote module within range of any other remote module.For example, remote module R11 will transmit on frequency F1 to remotemodule R13. Remote module R12 can simultaneously transmit on frequencyF2 to remote module R14. Remote modules R15, R16, R19 and R20 are alsotransmitting on their assigned frequencies F3, F4, F5, and F6,respectively. Remote module R20 sends its data packet to its basestation BS1. After the data packets are passed between the remotemodules, the transmit/receive states of the remote modules is reversed,as illustrated in the drawing by the next string of remotes. Remotemodule R23 transmits its data packet on frequency F7 and the processcontinues, with remote module R31 transmitting its packet to basestation BS2. Data is further transmitted down the backbone data link tothe central recording and control system.

It will thus be appreciated that the signals used by the modules aretime-division multiplexed and frequency division multiplexed. That is,as noted, modules within receiving range of one another that transmitduring the same time intervals may be assigned different transmissionfrequency bands to avoid interference. Thus, different modules withinreceiving range of one another and even within a single serial datatransfer path (e.g., the path defined by R11, R13, R15, R17, R19, R21,BS1 in FIG. 4) can transmit concurrently, thereby enhancing read outrates.

In addition, as noted above, any particular module may transmit onlyhalf of the time or less. For example, a module may transmit datasubstantially half of the time and receive data from an upstream moduleor modules substantially half of the time. Thus, within a given serialdata transfer path, adjacent modules will typically transmit in opposite(i.e., alternating) time intervals. Signals from adjacent modules willtherefore generally be time division multiplexed. As such, a givenfrequency band can be re-used by modules within receiving range of oneanother or even within a given serial data transfer path, therebyresulting in better use of the available data channels, which may allowfor greater density of the array (closer spacing of the modules) as maybe desired.

Moreover, it will be noted that each physical line of modules in FIG. 4is, in effect, defined by two (in the example of FIG. 4) or moreinterleaved serial data transfer paths. That is, the even number modulesassociated with base station BS1 (R12 . . . R20) define one serial datatransfer path and the odd number modules (R11 . . . R21) define another.These two serial data transfer paths may be coordinated so as to improvedata read out. For example, these serial data transfer paths may besynchronized so that modules R20 and R21 alternately transmit to basestation BS1. In this manner, resources are used more effectively as asingle antenna at base station BS1, operating with a substantially 100%duty cycle, can receive the signals from R20 and R21. Alternatively,base station BS1 can receive signals from spatially separated lines tomake a similarly effective use of resources. Although not shown in FIG.4, the base stations BS1 , BS2, etc., may receive data from separatelines, e.g., on opposite sides of the base stations.

It will be appreciated that the advantages of multiple multiplexingtechniques (e.g., time and frequency multiplexing) may be realized in avariety of ways. For example, rather than having the operation of agiven module be divided into two substantially equal intervals defininga cycle period (e.g., a receive interval followed immediately by atransmit interval), the cycle period may be divided into more than twointervals. For example, a module may receive data from a first upstreammodule during a first interval, receive data from a second upstreammodule in a second interval and transmit data (obtained at the moduleand/or received from the first and/or second upstream modules) in athird interval. For example, such a three interval cycle may be used inconnection with a nonlinear, serial data transfer layout. Alternatively,a three interval cycle may be used in connection with interleaving threeserial data transfer paths in a single physical line of modules as maybe desired.

Moreover, in some cases, modules may operate at less than a 100% dutycycle with respect to wireless data reception and transmission, i.e.,with quiet intervals within a cycle period where the module is neithertransmitting nor receiving. For example, the cycle may be divided intofour intervals, and odd numbered modules may receive in the firstinterval, transmit in the third interval and neither transmit norreceive in the second and fourth intervals. Even numbered modules mayreceive in the second interval, transmit in the fourth interval andneither transmit nor receive in the first and third intervals. Thisprovides a further dimension of time division multiplexing as betweenthe interleaved serial data transmission lines as may be desired, forexample, where efficient use of bandwidth is more critical thanfull-duty-cycle usage of any individual antenna.

Multiplexing technologies other than time-division and frequencydivision multiplexing may also be used, for example, code divisionmultiplexing. In code division multiplexing, a transmitter-receiver pairare assigned a digital code that enables a signal of interest to bedistinguished from other signals even where the other signals overlapthe signal of interest in time and frequency. The codes of potentiallyinterfering signals may be selected to be mathematically orthogonal soas to reduce interference. In the case of applications involving manypotentially interfering signals, long codes may be utilized, therebypotentially complicating processing and increasing overhead. In thepresent context, where low power transmissions and a well-defined arraygeometry are employed, shorter codes may suffice. Moreover, codedivision multiplexing may be combined with time division and/orfrequency division multiplexing as discussed above to further shortencodes and optimize processing. Additionally, depending on economicconsiderations amount other things, multiple antennae, for example,separate transmit and receive antennae, may be employed for a givenmodule.

In the example of FIG. 4, which involves a sampling rate of 500 samplesper second and a sampling resolution of 24 bits, remote module R11,transmitting half the time, must transmit data at 24000 bits per secondto remote module R13, which is currently acquiring data from its ownsensor at the 12000 bits per second rate. After some elapsed time, theremote modules all switch between transmitting and receiving status, andpass the data further down toward the base station. Now, remote moduleR13 will pass the data previously received from R11, plus its ownaccumulated data to remote module R15. Since it now needs to pass datafrom two sensors, the data rate will have to be 48000 samples per secondin order to prevent a backlog of data at the sensors. It will beappreciated that data originating form different modules, even though itis subsequently transferred in a single transmission interval, may havea slightly different reference time or time stamp as will be discussedin more detail below. Appropriate header or metadata may be associatedwith the data to not only identify the source module/location, but alsoto identify the acquisition time.

The required data rate will increase in a linear fashion as the line ofremote modules grows longer. When the number of stations in a linemultiplied by the sample rate times two exceeds the maximum data rate ofthe wireless data acquisition and relay modules, the line will no longerbe able to do keep up with the data flow. At that point, it will benecessary to add another line of base stations, or to allow delays inthe data transmission process, or allow “wait periods.” In the case of avibrating energy source, this would mean expanding the system componentsor stopping the energy source for the necessary delay. That is, in somecases, data may be stored at one or more of the modules or base stationsfor read out during repositioning of the energy source or at anothertime without delaying the survey process. Another option would be tocorrelate and/or stack the pilot signal from the vibrating energy sourcein the remote modules using the central processor, which greatly reducesthe amount of data required. Yet another option would be to use datacompression to reduce the number of data bits required to carry theinformation, which would allow the system to have more remote modulesper base station. When an explosive source is used to generate thevibration, the amount of seismic data collected in a time period is muchless, so arrays could be much larger than surveys that use a vibratingenergy source vehicle.

Each data packet from each remote module may contain information on thetime the data was collected, acquisition parameters, index number andserial number of the remote module, station coordinates, etc.Periodically, commands and information may be sent up or down the lineto the remote modules (e.g., time synchronization, acquisitionparameters, self-test instructions, etc.). The base station modules maycontain circuitry from multiple modules to allow data transmission totwo or more arrays in the same or different directions.

FIGS. 12A-12C graphically illustrate the serial transfer of seismic datapackets from a series of modules R1-Rn to a base station BS. Asillustrated, each module R1-Rn generates a data packet P1R_((1-n)) inresponse to at least a portion of a seismic event. The data in eachpacket P1R_(1-n)) is collected for a first time period T1. The firstpacket for each unit is then transmitted to another module disposedalong the serial data transfer path nearer to the base station BS. Theprocess is repeated for a second time period T2. However, it will benoted that the second module R2, in addition to generating a second datapacket P2R2 for the second time period T2, also is in receipt of thefirst packet P1R1 for the first time period as received from the firstmodule. See FIG. 12B. The first data packet P1R1 may be appended to thesecond data packet P2R2 for transfer to the third module R3 during thenext transmission period. In this regard, the data file transferred bythe second module R2 to R3 will include packets P1R1 and P2R2 fromdifferent modules (i.e., modules R1 and R2). Further, these packets P1R1and P2R2 will contain seismic data that is collected during two separatetime periods T1 and T2.

It will be appreciated that as the number of time periods increases, thenumber of data packets transferred by the last remote unit Rn to thebase unit BS may equal the number of remote units in the serial transferpath. For instance, the last module Rn may include a data packet fromeach module unit R(1-n). Further, each of these data packets may includedata for a different time period T(1-n). Accordingly, prior to utilizingthe packets from the module R(1-n), those packets will be correlated andreassembled. For instance the packets associated with the first moduleRI (e.g., P1R1 _(T1)-PnR1 _(Tn)) may be collated from multiple datafiles that were transmitted to the base station BS. The collated packetsmay be reassembled in temporal order to define a response of the firstmodule R1 to a seismic event. Of note, such collation and/or reassemblymay be performed by the base station, by the central control or at alocation remote from the seismic survey. In the latter regard, suchcollation and/or reassembly may be performed after the seismic survey iscompleted.

Frequencies are assigned to the modules in such a manner as to avoidinterference with other modules. Such assignment may depend the on knownlocation and separation of the modules, or may be based on automaticfield tests where actual experiments are conducted manually orautomatically by the central computer. Alternatively, the individualmodules might be instructed to conduct their own tests to determine thebest frequency allocation. In the case of weak signal strength, themodules might adjust their power output to the level necessaryconsistent with minimum use of battery power. In the event of anobstruction such as a ridge line, structure, or other problem with radiocommunication, one or more extra modules may be placed to maintain dataflow by acting as a radio relay. The extra module may or may not containa vibration sensor.

Data acquisition, the digitization of data from the sensors, and radiotransmission of previously acquired data will occur simultaneously sothere will be a small delay between acquisition and transmission.Accordingly, each packet of data may include information on the sourceand time of acquisition. The data packets will be reassembled into afile with records from all the sensors comprising the active portion ofthe array.

It will be appreciated that many variations of the systems of FIGS. 3and 4 are possible. One such system 800 is illustrated in FIG. 8. Theillustrated system 800 includes a generally rectilinear array ofacquisition modules 801 generally similar to that of the systems ofFIGS. 3 and 4. However, the illustrated system 800 includes multiplerows of base station modules, including a row of first base stationmodules 802 and a row of second base station modules 803. As discussedabove, a column of acquisition modules 801 transfers data in serialfashion to a base station 802 or 803. In this case, alternate columns ofacquisition modules 801 transfer data to opposite base stations 802 or803, as indicated by arrows 805. That is, if a given column transfersdata to a first base station 802, adjacent columns on either sidethereof transfer data to a second base station 803. There are variousarray design reasons why the array might be implemented in this fashion.For example, if a given data acquisition unit 801A is defective orotherwise off-line, data may be transferred around that module 801A byusing a module 801B of an adjacent column, as indicated by dashed lines806. For example, this may be implemented by appropriately adjusting thetransmit and/or frequencies of the relevant modules 801. In this regard,having adjacent columns read out in opposite directions is convenient soas to avoid the need to transfer undue amounts of data. That is, asnoted above, the amount of data transferred increases as you approach abase station in any column due to the serial data transfer protocol. Inthe illustrated case, modules 801 close to a base station are proximateto modules 801 in an adjacent column that are remote from theirrespective base stations. Accordingly, it will generally be possible touse a module 801B from an adjacent column as illustrated to bypass adefective module 801A without overloading the bypass module 801B. Inthis case, each module receiving data from bypass module 801B may onlyre-transmit data relevant to its serial data transmission line.

The illustrated base stations 802 and 803 transfer data to a centralcontrol and recording system 804 generally as described above. Also, asillustrated in FIG. 8, the base stations 802 and 803 may receiveinformation from modules 801 on either side thereof. For example, eachof the base stations 802 or 803 may have a pair of receivers forreceiving data from modules 801 on opposite sides thereof.

Turning now to FIG. 5, the wireless survey system 500 may provide forthe automatic determination of the location of the data acquisitionmodules. As shown, the system may utilize one or more Location FindingTechnology (LFT) systems 507, 509, 511 to determine the location of adata acquisition module 501. These LFT systems may employ a number oflocation finding technologies such as AOA, TDOA, GPS, signal strength orother methods. Examples of such systems include infrastructure-basedsystems such as AOA, TDOA and signal strength, external systems such asGPS, and hybrid systems such as infrastructure assisted GPS. Generally,an infrastructure-based system may determine the location of a dataacquisition module based on communications between the data acquisitionmodule and other wireless location units (WLUs) (e.g., dedicated LFTunits, other data acquisition modules, etc.). For example, and as willbe described in more detail below, such systems may receive informationconcerning a directional bearing of the data acquisition module or adistance of the module relative to one or more other WLUs. Based on suchinformation, the location of the data acquisition module may bedetermined by triangulation or similar geometric/mathematic techniques.External systems such as GPS systems, typically determine the locationof the data acquisition module relative to an external system (e.g., aGPS satellite constellation). This is accomplished by equipping the dataacquisition module with a GPS receiver.

Normally, the output from the LFT systems will be transferred to acentral control and processing system 505. The nature of the output andthe method of data transfer are described in more detail below.Generally, the output will include the location of one or more dataacquisition modules, and will be used by a data processor to process theseismic data into a format that can be analyzed.

For purposes of illustration, a number of different location findingtechnologies are depicted in FIGS. 6A-6C. FIG. 6A depicts time ofarrival (TOA) based LFT 600. In this case, the range between a firstdata acquisition module 601 and another WLU 603 is determined, based ontime of signal arrival or signal transmit time of a signal from a dataacquisition module to another WLU. Once the range between the dataacquisition module and at least three other WLUs 603, 605, 607 is known,the relative position of the first data acquisition module 601 can bedetermined by resolving the intersection of the ranges.

FIG. 6B generally illustrates an AOA based LFT system 610. AOA based LFTsystems may determine the location of a first data acquisition module611 based on the angle of arrival of signals 618, 619, generallyindicated by dashed lines 617, from the first data acquisition module asmeasured by two or more WLUs 613 and 615 which are equipped withantennas capable of resolving the angle of arrival of a signal, such asmultiple directional antennas (not shown). It will be appreciated thatmodules may therefore be equipped with specialized antennae for thispurpose. The various angles of arrival can be used to calculate thelocation of the first data acquisition module 611 based on theintersection of angles from two or more WLUs.

FIG. 6C illustrates a TDOA based LFT system 620. In TDOA systems,multiple WLUs 623, 625, 627 measure the time of arrival of signals froma first data acquisition module 621. Based on such measurements, thedifference of the time of arrival between two WLUs can provideinformation regarding the first data acquisition module's location interms of a hyperbola 629. The intersection of three or more of thehyperbolas 629 can be used to determine the location of the first dataacquisition module 621.

It will be appreciated that some of the methods described above providea relative location of a data acquisition module, that is, a locationrelative to one or more WLUs. In order to translate the relativelocation of the data acquisition module into an absolute one, theabsolute location of at least one WLU may be predetermined. This can beaccomplished using several methods. For example, one or more of the WLUsmay be equipped with a GPS receiver. As another example, the location ofone or more WLUs may be determined by any suitable method, and thelocation of the one or more WLUs may be used to translate the relativelocation into an absolute location.

Additionally, it is noted that the WLUs may be provided as any of anumber of suitable devices. As an example, in a preferred embodiment theWLUs may include other data acquisition modules and/or base stations. Inthis embodiment, the data acquisition modules would be configured toreceive signals from (or transmit signals to) surrounding dataacquisition modules (or base stations) for the purpose of automaticlocation. Alternatively, the WLUs may include receivers that arededicated to the function of locating the data acquisition modules.

It will be appreciated that the control and processing of the automaticlocation system may be performed at the central control and recordingsystem, or remotely. In one embodiment, the central control andrecording system may send a command to a first data acquisition module,directing it to start the automatic location procedure. This command maybe transferred in the same manner that the seismic data is transferred,or alternatively, may use a separate data transfer method. In otherwords, the data transfer structure for the automatic location system mayor may not be the same as is used for the transfer of seismic data. Nextthe first data acquisition module, or a separate control platform, maywirelessly send a command to surrounding data acquisition modulesindicating that they should prepare to receive a signal. Then the firstdata acquisition module may transmit a signal, and the surroundingmodules would receive it. The surrounding modules may then transfer theraw data (which may include identification, timing information, anglesof arrival, geographic coordinates, etc.) or processed information backto the central control and recording system using a suitable datatransfer method. In the case of raw data, the central control andrecording system may then use the information from the surroundingmodules to calculate the location of the first data acquisition moduleusing one or more of the methods described herein. Alternatively, thelogic to perform the location calculations may be included in the WLUs,or another suitable system. In the latter case, the WLUs may sendprocessed data that includes the location of one or more dataacquisition modules back to the central control and recording system.

As noted above, the system of the present invention can utilize avariety of multilateration technologies that have been developed inconnection with wireless telephony and mesh networks. However, thesystem of the present invention takes advantage of the seismic arraycontext to optimize these positioning technologies. In this regard, anexemplary seismic array 900 is illustrated in FIG. 9A. The array 900includes a number of acquisition modules 901. At least one of theacquisition modules 901A is self-locating, in this case, using an RFtechnology such as TDOA or signal strength. Such multilaterationtechnologies involve communication between the module to be located 901Aand multiple reference structures. For example, the multiple referencestructures may transmit signals to the module to be located 901A and/orthe module 901A may communicate signals to the reference structures. Inthis case, the reference structures may be other acquisition modules901B or dedicated reference structures 901C. For example, it may beconvenient to have some or all of the base stations 902 function as thereference structures 901C. Similarly, the signals used for locationpurposes may be dedicated location signals or may be data transfersignals including encoded information that can be used for positioningpurposes.

In the illustrated example, the module 901A receives positioning signalsfrom a number of other acquisition modules 901B. In this regard, themodule 901A may receive positioning signals from more than the minimumnumber of modules 901B required for three-dimensional positioning inorder to enhance positioning accuracy. Because the module 901A isstationary, it is not necessary that the various positioning signals bereceived at the same time. Thus, for example, the module 901A mayinclude an antenna that can be tuned to different frequencies atdifferent times so as to receive positioning signals from differentmodules 901B. Alternatively, the modules 901B may transmit positioningsignals at a designated frequency for module 901A. The transmittingstructures 901C, which may be other modules or base stations, may use ahigher transmission power for location signals than for seismic datatransfer signals so as to provide a longer transmission range. As lesslocation signals than seismic data transfer signals will generally beused, this can be done without undue depletion of batteries. It willthus be appreciated that the illustrated positioning system has a numberof advantages in relation to wireless telephony positioning systems dueto the array configuration and stationary nature of the array.

Further advantages in this regard are illustrated by FIGS. 9B and 9C. Asnoted above, certain multilateration technologies such as TDOA andsignal strength involve calculating ranges between the acquisitionmodule to be located and multiple external references. For purposes ofillustration above, such technologies were illustrated as involvingsimultaneously solving equations representing certain curves. Inreality, each of these ranging equations has an uncertainty, forexample, relating to uncertainties in time measurements or signalstrength measurements. This is graphically illustrated in FIG. 9B.Specifically, the uncertainties in these measurements correspond to afinite thickness envelope around each of the curves. As a result, thelocation of the acquisition module is defined by a shaded uncertaintyregion 900, representing the overlap of the thickness envelopes. Thus,in the illustrated example, there may be considerable uncertainty basedon resolving three range curves. Although the uncertainty region 900 isillustrated in two dimensions, it will be appreciated that theuncertainty region extends in three dimensions, all of which are ofinterest in relation to processing seismic data.

Due to the stationary nature of the seismic array, certain statisticalprocessing techniques can be used to reduce this uncertainty. This isillustrated in FIG. 9C. Specifically, FIG. 9C illustrates a plot of aseries of range determinations between an acquisition module to belocated and a given reference structure. The samples 902 may be takenover a period of time. It may be determined, theoretically orempirically, that these samples 902 define a Gaussian distribution orother defined distribution. Accordingly, statistical processes may beused to determine a projected actual range 903 based on the samples 902.This range is further depicted in FIG. 9B. By performing suchstatistical processes in relation to multiple reference structures, thelocation of the acquisition module of interest can be determined to therequired accuracy.

Another feature of the present invention involves a method for designinga seismic survey based on parameters that are unique to wireless seismicsurvey systems. Designing a wireless seismic survey system such as thepresent invention involves considerations that are different from thosepresent when designing a conventional wired system. For instance,various parameters for the wireless transfer protocol may be selected toachieve the desired performance (e.g., transmit power, antennasensitivity, number of channels to use, data transfer rate, etc.). As anexample, suppose a seismic survey is planned for a specific geographicarea. A designer may choose the spacing of the data acquisition modulesso as to achieve the desired resolution of the resulting seismic data.Then the transmit power and the number of wireless frequencies neededmay be selected. Furthermore, the data transfer rate may be chosen basedon the operating characteristics of the vibration source device, as wellas transmission duty cycle of the module and length of the serial datatransmission lines among other things. It will be appreciated that theexamples provided includes only a few of a number of various parametersthat may be considered when designing a wireless seismic survey system.

Additionally, choosing the layout of the data acquisition modules mayinvolve unique considerations when designing a wireless system. First,the layout of the modules is not constrained by the physical connectionof cables between each module. This may enable the designer to have moreflexibility when choosing a particular layout. For instance, thedistances between modules may be varied or randomized for variousreasons (e.g., to prevent aliasing of signals). Alternatively, thelayout may need to be an irregular pattern in order to avoidobstructions such as roads, bridges, rivers, buildings, etc.

Another feature of the present invention involves receiving seismic datafrom a wireless seismic survey system and processing and/or analyzingthe data into a form that is useful for resolving the characteristics ofone or more subsurface geologic structures.

The receiving step may include, for example, transferring the seismicdata to a computing system that is capable of processing the data. Inone embodiment, the computing system is the central control andrecording system. In another embodiment, the computing system is asystem other than the central control and recording system. In thelatter case, the seismic data may be transferred from the centralcontrol and recording system to the computing system by any suitablemethod (e.g., Ethernet, 802.11 wireless protocol, USB, Fire Wire,CD-ROM, hard disk drive, etc.). Additionally, it will be appreciatedthat the computing system may be geographically distant from the seismicsurvey site. For example, in one embodiment, the seismic data may beprocessed by a computing system in a different country from that whichthe seismic survey was carried out.

The processing step may include a number of methods for manipulating theseismic data (e.g., filtering, summing, synchronizing, displaying,etc.). Generally, the processing step involves manipulating the rawseismic data by a computing system into a form that is useful foranalysis. As an example, the output of the processing step may display a3D image of a subsurface geologic structure on a suitable displaydevice. As another example, the processing step may output frequencydata, such as data formatted for spectral analysis. Those skilled in theart will recognize that there are a number of algorithms that may beused to process seismic data into a useful form. Additionally, theprocessing step may include interpreting the seismic data obtained froma system such as the present invention to identify the characteristicsof one or more subsurface geologic structures. This portion of theprocessing step may be implemented by a computing system, or by a personqualified to interpret such data.

In practice, a seismic survey may be designed with reference to thecharacteristics of the wireless system. An associated process 1000 isillustrated in FIG. 10. In this regard, it is noted that there is aninterplay between the available bandwidth, the number of channelsutilized, the multiplexing technology or technologies used andassociated antenna duty cycle, and transmitter power. Thus, for example,based on the objectives of the survey, the geographical extent of thesurvey may be determined (1002). It will be appreciated that there maybe some flexibility regarding the exact geographical extent of thesurvey, as well as the number and spacing of the data acquisitionmodules. In this regard, the designer may determine (1004) the totalbandwidth that is available for use by the acquisition modules anddetermine (1006) the desired channel width for the communicationchannels used by the acquisition modules. It may be desired to providesome buffer between adjacent channels to avoid interference.

Based on the total bandwidth available and the desired channel width,the total number of channels that are available for the system can bedetermined (1008). In addition, the designer can determine (1009) themultiplexing technology or technologies to be used, for example, timedivision and frequency division multiplexing as described above. Thedesigner can also determine (1010) the read out time that is desired forthe array. For example, in the case of a vibrating energy source, it maybe desired to complete read out of the array in approximately 20 secondsso as to avoid delaying operation of the source and completion of thesurvey.

Based on all of this information, as well as the technical specificationof the modules and other array equipment, the designer can perform anumber of calculations to determine possible array configurations. Forexample, the designer can calculate (1012) how many modules can be in aserial data transfer path. Thus, in the example described above, themodules were sampled at a rate of 500 samples per second with aresolution of 24 bits per sample. Further, each module was assumed totransmit half of the time. As a result, the first module transmits dataat a rate of n (in this case, 24000 bits per second), the second moduletransmits at 2n (in this case, 48000 bits per second), the third moduletransmits at 3n (in this case, 72000 bits per second), etc., in order toprevent a backlog of data at the modules. Accordingly, there will besome maximum serial data transfer path length at which the data transferrate required will equal the maximum data transfer rate specification ofthe modules. For example, if the module specification is 1 Mbit/sec.,the maximum length of a serial data transfer path may be about 40modules. The designer may use this parameter to calculate the maximumnumber of modules in a serial data transfer path and, hence, howfrequently “backbones” of base stations or other storage/transfer unitswill be required. In the example, where two serial data transfer pathsare interleaved in a single physical line of modules associated with agiven base station, the length of the physical line, in terms of numberof modules, will be twice the length of a serial data transfer path.

However, using the assumption, for ease of illustration, that datatransfer rates are independent of module spacing, the configuration ofthe array can still vary considerably. Specifically, it is stillnecessary for the designer to determine the spacing between modules in aphysical line, the spacing between lines, and the total number ofmodules to be used in the array. Conventionally, for a broad range ofseismic surveys, the spacing between modules in a line may be on theorder of 25-100 m, and the spacing between lines may be on the order of100-400 m. The spacings selected are typically based on weighting thedesire for improved imaging resolution against the increased surveyexpense associated with using a longer number of modules.

In the case of the wireless system described herein, it is anticipatedthat survey expense may be reduced and designers may, therefore, desireto use a denser array of modules. However, this requires that suchincreased density be accommodated without unacceptable signalinterference between the modules. Accordingly, the designer maycalculate (1014) the array density that can be achieved withoutunacceptable interference. For example, this may be calculated as afunction of how many communication channels are available, how oftenthey can be reused as a function of geometric space and how often theycan be reused as a function of any multiplexing technology employedbeyond frequency division multiplexing.

It will be appreciated that these parameters will be affected by avariety of factors such as external sources of interference, thetopology of the survey landscape including any obstructions, and thelike. Moreover, one of the advantages of the present invention is thatlaborers are not required to precisely position the modules, so actualpositions may vary. Additionally, the transmit powers can be varied,before or after array deployment, and the array can be self-configuringbased on expected or actual signal strength. Accordingly, someuncertainty may be accounted for in array design.

In a simple example, however, a designer may assume that channels may bereused by modules no closer than 400 m from one another (transmit powersmay be tuned after deployment to match this specification). Moreover,based on the available bandwidth spectrum and the channel width requiredby the array equipment, the total number of channels available may bedetermined as discussed above. Based on this information, the designercan calculate (1016) intra and inter line spacing of modules. Inpractice, this may be affected by any directionality of the antennae andother factors.

For purposes of illustration, it may be assumed that 100 channels areavailable and that the antennae have no directional selectivity.Moreover, because only half of the modules are transmitting at any giventime, the 100 channels may be reused by modules within 400 m of oneanother, provided that the channels are not used at the same time.Accordingly, 200 channel/time slots are available within a circle of 400m radius (assuming no interference from adjacent regions of the array).Accordingly, if an interline spacing is desired that is four times theintraline spacing, it may be determined that an intraline spacing ofabout 25 m and an interline spacing of 100 m can be accommodated.Assuming that the survey objectives can at least be satisfied by thewireless array, the designer can then select (1018) a layout that is atleast sufficient for the survey objectives and within the interferencelimits of the wireless array and/or can select (1020) a transmitterpower for the acquisition units to achieve the survey objectives withoutundue interference. Once the general parameters of the array are thusestablished, the designer can determine (1022) the array configuration(addressing, for example, topography and obstructions) and can assignchannels to the various acquisition units.

It will be appreciated that the processing of the data from the wirelessarray will also take into account the nature of the wireless system.Such processing may be executed locally at the survey location and/orremotely. For ease of reference, the following discussion references aprocessor, though multiple machines at multiple locations may beinvolved in such processing. An associated process 1100 is summarized byreference to the flow chart of FIG. 11. In the illustrated example, theprocessor receives (1102) the read out data from the array. It will beappreciated that, due to the read out process described above, this datawill not be received in proper time sequence. That is, a first, or mostremote, module in a serial data transfer path transmits data for timeperiod n to an adjacent second module. That module then retransmits thatdata from the first module for time period n together with data acquiredby the second module for time period n+1. This process continues downthe serial data transfer path such that packets for different modulesthat form a single data stream have different time stamps.

Accordingly, the processor sorts (1104) the data by acquisition time.The processor then collects (1106) data from the modules associated witha common time. These steps of receiving, sorting and collecting may berepeated until data from the array is obtained corresponding to the timeperiod of a detected seismic event. The data from any one of the modulesfor this time period thus defines a trace.

Processing of these traces generally requires knowledge of the time andlocation parameters of the data. As discussed above, the data packetswill have time stamps that allow for correlation of data obtained atdifferent modules at the same time. In this regard, reference timesignals can be provided from a common system clock (or other timesources(s)) and synchronization, as between modules, is maintained viacontrol signals transmitted serially across the array as discussedabove. Accordingly, the processor stores (1108) time parameterinformation for the data by way of the time stamps or a packet-by-packetbasis in the context of the present invention.

The process also receives (1110) location parameter information for thedata. This information and the processing thereof is also a function ofthe location finding system context of the array. That is, as notedabove, this information may be based on a multilateration process andmay be statistically processed for improved accuracy. Accordingly, theinformation may be developed over time and may be dependent on knowledgeof the location of other modules or position references, which knowledgemay also be developed over time. Accordingly, at least with respect toinitially acquired data, the location information may not beconcurrently available. Rather, the header information or other metadatamay simply identify a module, such that location informationcorresponding to that module can be later associated with the data.

Accordingly, the processor receives data with time and locationparameter information associated therewith in a manner unique to thewireless context of the array. It will further be appreciated that thenature of the data may be a function of this wireless context, e.g., thearray may be denser than normally utilized for wired arrays. Moreover,the associated processing may involve demultiplexing and noise reductionfiltering as a function of the wireless context. The processor thenprocesses (1112) the resulting data in conventional fashion to obtaininformation regarding subterranean structure. For example, suchprocessing may involve normal moveout, trace stacking, etc.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and description isto be considered as exemplary and not restrictive in character. Forexample, certain embodiments described hereinabove may be combinablewith other described embodiments and/or arranged in other ways (e.g.,process elements may be performed in other sequences). Accordingly, itshould be understood that only the preferred embodiment and variantsthereof have been shown and described and that all changes andmodifications that come within the spirit of the invention are desiredto be protected.

1. A method for use in seismic data acquisition, comprising the stepsof: disposing, in series, a plurality of seismic data acquisitionmodules that are operative to wirelessly communicate acquired seismicdata, wherein said acquisition modules define a wireless serial datatransfer path for relaying data from upstream acquisition modules todownstream acquisition modules and a data collection unit; assigning afirst acquisition module in said serial data transfer path a firsttransmission frequency; assigning a second acquisition module in saidserial data transfer path a second transmission frequency, wherein saidfirst and second transmission frequencies are different.
 2. The methodof claim 1, further comprising: first transmitting, on said firsttransmission frequency, seismic data from said first acquisition moduleto at least one downstream acquisition module; and second transmitting,on said second transmission frequency, seismic data from said secondacquisition module to at least one downstream acquisition module.
 3. Themethod of claim 2, wherein at least a portion of said first transmittingand at least a portion of said second transmitting occur during a commontransmission period.
 4. The method of claim 2, wherein said firsttransmitting comprises said first acquisition transmitting said seismicdata to said second acquisition module.
 5. The method of claim 4,wherein said second transmitting comprises: receiving a first set ofseismic data from said first acquisition module; appending a second setof seismic data from said second acquisition module; and transmittingsaid first and second sets of seismic data to a downstream acquisitionmodule.
 6. The method of claim 1, further comprising: assigning saidfirst transmission frequency to a third data acquisition module.
 7. Themethod of claim 6, wherein said first and third acquisition modules arepositioned in said serial data transmission path at first and secondlocations, and wherein a distance between said first and secondlocations is greater than a transmission range of said first and thirdacquisition modules.
 8. The method of claim 6, wherein said thirdacquisition module is within a transmission range of said firstacquisition module.
 9. The method of claim 8, wherein said thirdacquisition module is operative to transmit seismic data during atransmission period that is temporally distinct from a transmissionperiod of said first acquisition module.
 10. The method of claim 8,wherein said third acquisition module form part of a different datatransmission path, wherein said first and third acquisition modules arein a common seismic array.
 11. The method of claim 10, wherein saidthird acquisition module is disposed in a second serial data transferpath. 12.-35. (canceled)
 36. A method for use in seismic dataacquisition, comprising: disposing a plurality of seismic dataacquisition modules in an array, wherein each seismic data acquisitionmodule is operative to wirelessly communicate with at least one otherseismic data acquisition module in said array to define at least a firstserial data transmission path; assigning each of said plurality ofseismic data acquisition modules in said first serial data transmissionpath a transmission frequency for use in transmitting said seismic data,wherein at least one transmission frequency is assigned to first andsecond seismic data acquisition modules in said first serial datatransmission path; during a common transmission period, transmittingseismic data from said first and second seismic data acquisition unitsusing said at least one transmission frequency.
 37. The method of claim36, wherein said first and second seismic data acquisition units arepositioned is said first serial data transmission path at first andsecond locations, and wherein a distance between said first and secondlocations is greater than a transmission range of said first and secondseismic data acquisition units.
 38. The method of claim 37, furthercomprising: adjusting a transmission power of at least one of said firstand second seismic data acquisition units such that a transmission rangeof said at least one seismic unit acquisition unit is less than saiddistance between said first and second locations.
 39. The method ofclaim 36, further comprising: identifying a number of availabletransmission frequencies; and assigning said available transmissionfrequencies in a repeating series to said seismic data acquisition unitsin said first serial data transmission path.
 40. The method of claim 36,further comprising: assigning said at least one transmission frequencyto a third seismic data acquisition unit within a transmission range ofone of said first and second seismic data acquisition units.
 41. Themethod of claim 40, wherein said third seismic data acquisition unit isoperative to transmit seismic data during a transmission period that istemporally distinct from said common transmission period.
 42. The methodof claim 40, wherein said third data acquisition unit forms a portion ofa second serial data transmission path separate from said first serialdata transmission path.
 43. The method of claim 36, wherein saidplurality of data acquisition units are disposed in a linear array. 44.The method of claim 36, wherein said first serial transmission path isaligned with said linear array. 45.-69. (canceled)
 70. A method for usein seismic data acquisition, comprising: disposing a plurality ofseismic data acquisition modules in series, wherein each seismic dataacquisition module is operative to wirelessly communicate with at leastone other seismic data acquisition module for purposes of serial relayof seismic data; receiving at one of said seismic data acquisitionmodules, upstream seismic data from at least one upstream seismic dataacquisition module, wherein said upstream data is received on a firsttransmission frequency; transmitting from said one seismic dataacquisition module said upstream seismic data to a downstream seismicdata acquisition module, wherein said upstream seismic data istransmitted on a second transmission frequency, wherein said first andsecond transmission frequencies are different.
 71. The method of claim70, further comprising: appending seismic data generated by said oneseismic data acquisition module to said upstream data prior totransmitting said upstream seismic data.
 72. The method of claim 70,wherein receiving comprises receiving said upstream data from anon-adjacent upstream seismic data acquisition module in said series ofseismic data acquisition modules.
 73. The method of claim 70, whereintransmitting comprises transmitting said upstream data to a non-adjacentdownstream seismic data acquisition module in said series of seismicdata acquisition modules. 74.-138. (canceled)
 139. An apparatus for usein seismic data acquisition, comprising: a plurality of seismic dataacquisition modules, disposed in series, operative to wirelesslycommunicate acquired seismic data, wherein said acquisition modulesdefine a wireless serial data transfer path for relaying data fromupstream acquisition modules to downstream acquisition modules and adata collection unit; a first acquisition module in said serial datatransfer path for transmitting seismic data using a first transmissionfrequency; and a second acquisition module inset serial data transferpath for transmitting seismic data using a second transmissionfrequency, when said first and second transmission frequencies aredifferent.
 140. The apparatus of claim 139, wherein said firstacquisition module and said second acquisition module are operative totransmit seismic data during a common transmission,
 141. The apparatusof claim 139, further comprising a third data acquisition module in saidserial data transfer path for transmitting seismic data using said firsttransmission frequency.
 142. The apparatus of claim 141, wherein saidand first and third acquisition modules are positioned in said serialdata transfer path at first and second locations, wherein a distancebetween said first and second locations is greater than a transmissionrange each of each of said first and third acquisition modules.
 143. Theapparatus of claim 141, wherein said third acquisition module is withina transmission range of said first acquisition module and said firstacquisition modules operative to transmit seismic data during atransmission period that is temporally distinct from a transmissionperiod of said third acquisition module.